A Pakistani teenager moved a translator to tears on Capitol Hill as he spoke of the moment his grandmother was killed in a US drone strike.

Zubair ur Rehman, 13, who attended the event with his father Rafiq and his sister Nabila, aged nine, described how Momina Bibi, 67, was out picking okra when a drone fired several missiles at an unknown targets near his compound.

He said he first heard the drone hovering overhead but was not concerned because neither he nor his grandmother were militants.

â€œWhen the drone fired the first time, the whole ground shook and black smoke rose up. The air smelled poisonous. We ran, but several minutes later the drone fired again,â€ he said at the congressional briefing.

â€œPeople from the village came to our aid and took us to hospital. We spent the night in great agony in at the hospital and the next morning I was operated on. That is how we spent Eid.

â€œNow I prefer cloudy days when the drones donâ€™t fly. When the sky brightens and becomes blue, the drones return and so does the fear. Children donâ€™t play so often now, and have stopped going to school. Education isnâ€™t possible as long as the drones circle overhead.â€

His sister, Nabila, who held up a picture she drew depicting the strike above her village, told the various members of Congress who attended the event: â€œEverything was dark and I couldnâ€™t see anything. I heard a scream. I think it was my grandmother but I couldnâ€™t see her.

His father told various members of Congress who attended the event that nobody had ever told him why his mother was targeted on October 24, 2012, in Pakistanâ€™s North Waziristan province.

â€œSome media outlets reported that the attack was on a car, but there is no road alongside my motherâ€™s house. Others reported that the attack was on a house. But the missiles hit a nearby field, not a house. All of them reported that three, four, five militants were killed,â€ he said.

The use of drones to fight the war on terror has intensified markedly under Barack Obama as the number of troops on the ground in Afghanistan and the Pakistani tribal areas has been scaled back prior to a complete drawdown in 2014.

It remains a major source of tension between the US and Pakistan, with Nawaz Sharif, Pakistanâ€™s prime minister, calling for an end to US drone strikes during his first meeting with President Barack Obama at the White House last week.

Mr Sharif was elected over the summer on a promise to halt Americaâ€™s drone campaign, which a report by Amnesty International estimated has killed 900 civilians in Pakistan â€“ a figure that is disputed by the US government.

The story of the Rehman family is featured in a new film on the human cost of drones strikes, â€œUnmanned: Americaâ€™s Drone Warsâ€, by Robert Greenwald of Brave New Foundation which is released on Wednesday.